Spark igniter



Feb. 18, 1969 a. H. PINCKAERS SPARK IGNITER Filed 001;. 25, 1967 VALVEl6 ATTORNEY.

3,428,823 SPARK IGNITER Balthasar H. Pinckaers, Edina, Minn., assignorto Honeywell Inc., Minneapolis, Minn., a corporation of Delaware FiledOct. 25, 1967, Ser. No. 677,992 U.S. Cl. 307106 Int. Cl. F23n 5/00; H03k3/00 Claims ABSTRACT OF THE DISCLOSURE A spark igniter having a step-upignition transformer whose secondary winding is connected in a closedseries circuit with the primary winding of a second transformer, thewinding of a valve, and a high impedance resistor across which sparkignition electrodes are connected; hav-- ing a low voltage sourceconnected to apply a low-voltage checking pulse to the primary windingof the ignition transformer to cause a circulating current to flowthrough the above mentioned series circuit if circuit continuity exists;and having a high-voltage ignition pulse source connected to becontrolled by the secondary winding of the second transformer to apply ahigh voltage pulse to the primary winding of the ignition transformeronly if circuit continuity exists.

Background of the invention My invention relates to the art of sparkigniters and t0 means to check for the existence of a spark. In mycopending application Ser. No. 602,641, filed Dec. 19, 1966, for a SparkProving and Utilization Device and System, I disclose a spark igniterwhich insures that a spark exists in the high voltage circuit andutilizes the rectification effect of the spark to charge a capacitorconnected in parallel with a fuel valve. With the device of my copendingapplication, the valve will not open when the spark electrodes areshorted. I have since found that if a double failure occurs wherein thespark electrodes are shorted, and at the same time a spark-sustainingopen circuit occurs in series with the spark electrodes, the fuel valvemay still open.

The present invention is directed to means to detect the existence of anopen circuit, in the high voltage circuit, which may exist at other thanthe ignition spark gap, and to render the spark igniter inoperative(fail-safe) in the presence of such an unintentional open circuit.

Summary of the invention The present invention utilizes a high impedanceshunt for the ignition electrodes connected in closed series circuitwith the secondary winding of the ignition transformer together withmeans to apply a low-voltage checking pulse to the series circuit tocheck circuit continuity, and means controlled as a result of circuitcontinuity to apply a high-voltage ignition pulse to the series circuit.

More specifically, a first capacitor is connected to be charged to ahigh voltage during a first half cycle of an AC source, the discharge ofthis capacitor through the primary winding of the ignition transformerbeing controlled by switch means. A second capacitor is connected to becharged during the alternate half cycle of the AC source. Low-voltageresponsive means effects a discharge of the second capacitor through theprimary winding of ice the ignition transformer early in the alternatehalf cycle; whereupon, if circuit continuity exists, the switch means isactuated and the first capacitor is discharged to cause a spark to occurduring the alternate half cycle.

Brief description of the drawing The single figure is a schematicshowing of the preferred embodiment of my invention.

Description of the preferred embodiment Referring to the single figure,reference numeral 10 designates a high-voltage, step-up ignitiontransformer having a secondary winding 11 and a primary winding 12. Theprimary winding is energized from conductors 13 and 14 which are adaptedto be connected to a source of AC voltage, not shown. Secondary winding11 is connected to terminals 41 and 42 which are adapted to be connectedto ignition electrodes 15 to apply a high voltage in the range of 10,000volts to these electrodes to cause an ignition spark to occur at thespark gap which separates the electrodes. Electrodes 15 are adapted tobe associated with a fuel burner, not shown, to ignite fuel flowing fromthe fuel burner. Reference numeral 16 identifies generally a valve,shunted by capacitor 17, to allow fuel to flow to the burner when thevalve is energized. In accordance with the teachings of my abovementioned copending patent application, valve 16 is energized only whenspark exists at a gap in the high voltage circuit, intended to be atelectrodes 15.

A first capacitor 20 is connected to conductors 13 and 14 by a circuitincluding diode 50. Capacitor 20 is charged to a high voltage during thehalf cycle of the AC source in which conductor 13 is positive, the upperterminal of the capacitor being positive with respect to the lowerterminal. This half cycle of the AC source will be designated the firsthalf cycle.

The discharge of capacitor 20 through the primary winding of transformer10 is controlled by switch means 26 in the form of an SCR having anoutput circuit 27, 28 and an input circuit 28, 29.

A second capacitor 21, shunted by diode 22, is connected to conductors13 and 14 by a circuit including resistor 23. During the above mentionedfirst half cycle, diode 22 conducts to short capacitor 21. During thesecond half cycle, when conductor 13 is negative, capacitor 21 charges,the left-hand terminal being positive with respect to the right-handterminal. Reference numeral 24 identifies a voltage responsive switch inthe form of a breakdown diode, such as a four-layer diode. This switchresponds to the presence of a low voltage on capacitor 21, for example10 volts, and becomes conductive to discharge capacitor 21 through diode25 and the primary winding of transformer 10.

Reference numeral 30 identifies current responsive means in the form ofa transformer having a primary winding 31 and a secondary winding 32.The primary winding of this transformer is connected in a closed seriescircuit with the secondary winding of ignition transformer 10, thewinding of valve 16 and a high magnitude impedance 40 which is connectedto terminals 41 and 42 and is adapted to shunt ignition electrodes 15.Specifically, impedance 40 is a resistor which may, for example, have amagnitude of 1 megohm.

The secondary winding of transformer 30 is connected to the inputelectrodes 28, 29 of SCR 26.

Considering now the operation of the preferred embodiment, on the firsthalf cycle of AC source 13, 14, capacitor 20 charges to a high voltage,the upper terminal of the capacitor being positive with respect to thelower terminal. On the second half cycle of the AC source, capacitor 21charges through resistor 23. Early in this second half cycle, capacitor21 reaches a charge to cause diode 24 to break down. Thus, capacitor 21discharges through the circuit including diode 25 and the primarywinding of ignition transformer 10. This discharge produces a lowmagnitude voltage checking pulse which circulates a current through theclosed series circuit 11, 40, 16, and 31. It is of significance that themagnitude of this checking pulse does not produce a spark at electrodes15 and would likewise not produce a spark at an open circuit which mightexist in the above mentioned closed series circuit. Furthermore, thischecking pulse does not result in the energization of valve 16 even ifelectrodes 15 are shorted.

A circuit discontinuity, such as in the secondary winding of theignition transformer, may well be of the type which would, at the higherignition pulse voltage, allow a spark to exist at the discontinuity oropen, and then valve 16 would be energized even if the electrodes 15 areshorted. The purpose of the checking pulse is to insure that in fact nosuch discontinuity exists. This is done by making continuity in the highvoltage circuit a pre-condition for applying the higher ignition pulsevoltage. The electrodes 15 may be shorted but this already prevents thevalve 16 from being energized in accordance with the teaching of mycopending application.

With my present invention, an output exists at the secondary winding oftransformer 31 as a result of the checking current pulse only whencircuit continuity exists.

The secondary winding of transformer 31 is then effective to render SCR26 conductive during this same second half cycle of AC source 13, 14.Thus, during the same second half cycle, capacitor 20 discharges throughthe primary winding of ignition transformer 10 and a high voltageignition pulse is supplied to the above mentioned closed series circuit.In this event, however, the high voltage produces a spark at electrodes15.

In accordance with the teachings of my above copending application,valve 16 is energized to allow fuel to flow to the burner only when aspark exists, the spark producing a unidirectional current in the abovementioned series circuit, to charge capacitor 17 and maintain valve 16energized and open.

While I have shown a specific means of achieving a low voltage checkingpulse and a high voltage ignition pulse, the practice of my inventiondoes not require these specific means. My invention requires the highmagnitude impedance 40 to shunt ignition electrodes 15 to form a closedseries circuit through which a lowvoltage checking pulse current maycirculate when circuit continuity exists, along with current responsivemeans 30 to respond to this circulating current to then cause a highvoltage ignition pulse to be applied to the series circuit to produce aspark at electrodes 15.

With the structure of the preferred embodiment of my invention, onespark is produced at electrodes 15 for each line cycle. Thus, shouldsource 13, 14 be a 60-cycle per second source, 60-pulses per second willbe produced at electrodes 15.

Theembodiments of the invention in which an exelusive property or rightis claimed are defined as follows:

1. A spark igniter for use with spark ignition means, comprising;

a step-up ignition transformer having a primary winding and a secondarywinding,

a pair of terminals connected in circuit with said secondary winding andadapted to be connected to the spark ignition means, an impedanceconnected between said terminals to complete a circuit through saidsecondary winding,

ignition-pulse generating means having an input to initiate operationthereof, and having a high volt age output connected to said primarywinding,

checking-pulse generating means having a low voltage output connected toproduce a low voltage current flow through said circuit including saidsecondary winding and said impedance,

and current responsive means responsive to said current flow andconnected to control said input to initiate operation of saidignition-pulse generating means.

2. A spark igniter as defined in claim 1 wherein said checking-pulsegenerating means is connected to said primary winding and said currentresponsive means is connected in circuit with said secondary winding andsaid impedance.

3. A spark igniter as defined in claim 1 wherein said current responsivemeans is a transformer having a first winding connected in circuit withsaid secondary winding and said impedance, and having a second windingconnected to said input.

4. A spark igniter as defined in claim 1 wherein said ignition-pulsegenerating means includes a capacitor and circuit means adapted tocharge said capacitor to a high voltage, and includes a controllableswitch to discharge said capacitor through said primary winding, andwherein said current responsive means is connected to control saidswitch.

5. A spark igniter as defined in claim 4 wherein said current responsivemeans is a transformer having a first winding connected in circuit withsaid secondary winding and said impedance, and having a second windingconnected to control said switch.

6. A spark igniter as defined in claim 1 wherein said checking-pulsegenerating means includes a capacitor and circuit means adapted tocharge said capacitor, and means including a low-voltage responsiveswitch connecting said capacitor to said circuit including saidsecondary winding and said impedance.

7. A spark igniter as defined in claim 6 wherein said low-voltageresponsive switch is connected to said primary winding to discharge saidcapacitor through said primary winding when said capacitor is charged tothe low voltage.

8. A spark igniter as defined in claim 7 wherein said current responsivemeans is a transformer having a first winding connected in circuit withsaid secondary winding and said impedance, and having a second windingconnected to said input.

9. A spark igniter as defined in claim 1 including terminal meansadapted to be connected to a source of AC voltage; wherein saidignition-pulse generating means includes a capacitor and circuit meansconnected. to said terminal means and adapted to charge said capacitorto a high voltage during a first half cycle of the AC source, andfurther includes a controllable switch to discharge said capacitorthrough said primary winding; wherein said current responsive means isconnected to control said switch; and wherein said checking-pulsegenerating means includes a second capacitor and circuit means connectedto said terminal means and adapted to charge said second capacitorduring the opposite half cycle of the AC source, and further includesmeans including a low-voltage responsive switch connecting said secondcapacitor to said circuit including said secondary winding and saidimpedance.

10. A spark igniter as defined in claim 9 wherein said low-voltageresponsive switch is connected to said primary winding to discharge saidsecond capacitor through said primary winding during said opposite halfcycle; and wherein said current responsive means is a trans- ReferencesCited UNITED STATES PATENTS 2,628,676 2/1953 Shottenfeld 43166 63,277,949 10/ 1966 Walbridgc 431-6 3,291,183 12/1966 Fairiey 431663,384,439 5/1968 Walbridgc 43124 5 CHARLES J. MYHRE, Primary Examiner.

R. A. DUA, Assistant Examiner.

US. Cl. X.R.

